<template>
  <div>
    <div class="alphabet">
      <ul>
        <li v-for="item in letters" :key="item" :ref="item"
            @click="handleLetterClick"
            @touchstart="handleTouchStart"
            @touchmove="handleTouchMove"
            @touchend="handleTouchEnd"
        >{{ item }}
        </li>
      </ul>
    </div>
  </div>
</template>

<script>
export default {
  name: 'Alphabet',
  data () {
    return {
      touchStatus: false,
      startY: 0,
      timer: null
    }
  },
  updated () {
    this.startY = this.$refs['A'][0].offsetTop
  },
  computed: {
    letters () {
      const letters = []
      for (let i in this.cities) {
        letters.push(i)
      }
      return letters
    }
  },
  methods: {
    handleLetterClick (ev) {
      this.$emit('change', ev.target.innerText)
      // console.log(ev.target.innerText)
    },
    handleTouchStart () {
      this.touchStatus = true
    },
    handleTouchMove (e) {
      if (this.touchStatus) {
        if (this.timer) {
          clearTimeout(this.timer)
        }
        this.timer = setTimeout(() => {
          // const startY = this.$refs['A'][0].offsetTop
          const touchY = e.touches[0].clientY - 79
          const index = Math.floor((touchY - this.startY) / 20)
          if (index >= 0 && index < this.letters.length) {
            this.$emit('change', this.letters[index])
          }
        }, 16)
      }
    },
    handleTouchEnd () {
      this.touchStatus = false
    }
  },
  props: ['cities']
}
</script>

<style lang="stylus" scoped>
  .alphabet
    position: absolute
    top: 1.58rem
    right: 0
    bottom: 0
    display flex
    flex-direction column
    justify-content center
    //使用了better-scroll这里必要明确设置宽,不然就滚动不了。俺也不知这是为何????
    width: .4rem

    ul
      line-height: .4rem
      color: #00bcd4
      text-align center
</style>
